EP0382831B1 - Chemically sensitive transducer - Google Patents

Chemically sensitive transducer Download PDF

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Publication number
EP0382831B1
EP0382831B1 EP89908966A EP89908966A EP0382831B1 EP 0382831 B1 EP0382831 B1 EP 0382831B1 EP 89908966 A EP89908966 A EP 89908966A EP 89908966 A EP89908966 A EP 89908966A EP 0382831 B1 EP0382831 B1 EP 0382831B1
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EP
European Patent Office
Prior art keywords
transducer according
measuring electrode
substrate plate
transducer
membrane
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP89908966A
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German (de)
French (fr)
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EP0382831A1 (en
Inventor
Norbert Hampp
Christoph BRÄUCHLE
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BRAEUCHLE, CHRISTOPH
HAMPP, NORBERT
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Individual
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Priority to AT89908966T priority Critical patent/ATE85430T1/en
Publication of EP0382831A1 publication Critical patent/EP0382831A1/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403—Cells and electrode assemblies
    • G01N27/414—Ion-sensitive or chemical field-effect transistors, i.e. ISFETS or CHEMFETS
    • G01N27/4148—Integrated circuits therefor, e.g. fabricated by CMOS processing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/4805—Shape
    • H01L2224/4809—Loop shape
    • H01L2224/48091—Arched
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/73—Means for bonding being of different types provided for in two or more of groups H01L2224/10, H01L2224/18, H01L2224/26, H01L2224/34, H01L2224/42, H01L2224/50, H01L2224/63, H01L2224/71
    • H01L2224/732—Location after the connecting process
    • H01L2224/73251—Location after the connecting process on different surfaces
    • H01L2224/73265—Layer and wire connectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/30—Technical effects
    • H01L2924/301—Electrical effects
    • H01L2924/3011—Impedance
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/30—Technical effects
    • H01L2924/301—Electrical effects
    • H01L2924/3025—Electromagnetic shielding

Definitions

  • the invention relates to a chemosensitive transducer for the selective determination of a chemical property of a fluid, with at least one field effect transistor, the gate of which is connected to an associated measuring electrode which is covered with a membrane sensitive to the chemical property, and with an encapsulation which covers the entire transducer with the exception of the membrane isolated from the fluid.
  • “Chemosensitive” means three an ion- or gas-sensitive property, a sensitivity for enzyme substrates, for antibodies / antigens or for hydride-capable DNA / RNA groups. Depending on their sensitivity, such transducers can be used in medicine, for example for blood analysis, in clinical chemistry, for therapy control, hormone determination, infection and tumor diagnosis, and also in fermentation control, food analysis, and environmental analysis, as well as for process control.
  • a chemosensitive transducer with the features specified in the preamble of claim 1 is known from EP-B-0 065 350.
  • a field effect transistor is formed in a semiconductor substrate, the gate of which is connected via a laterally adjoining conductor to a measuring electrode arranged on the same side of the substrate.
  • the measuring electrode is one for the existing chemical Provide property sensitive membrane or layer, which is applied by electroplating, sputtering or vapor deposition.
  • the field effect transistor is encapsulated against the fluid to be examined by a protective layer which consists of an epoxy resin or silicone rubber.
  • a corresponding output signal can be obtained by potentiometric or amperometric measurement, which is proportional to the concentration of the parameter to be measured.
  • the voltage caused by the ion exchange reaction mentioned is in the mV range, but the ohmic load capacity of the membrane is in the pA to fA range.
  • Another difficulty with the known transducers is that they can only be used for the detection of chemical properties for which membranes are sensitive, which can be applied to the measuring electrode by the methods mentioned.
  • the invention has for its object to provide a chemosensitive transducer which has a higher sensitivity compared to known chemosensitive transducers, and which is at the same time insensitive to electrical influences as well as to temperature fluctuations, it should also be sensitive to those properties that can only have it detected with less stable membrane substances.
  • a carrier plate is provided, on one side of which the measuring electrode and on the other side of which an amplifier circuit containing the field effect transistor are arranged; furthermore, the measuring electrode is electrically connected to the gate of the field effect transistor via a conductor passing through the carrier plate.
  • the arrangement of the measuring electrode and amplifier circuit on opposite sides of a carrier plate with plated-through holes through the carrier plate results in the shortest distances between the respective measuring electrode and the associated amplifier circuit with a correspondingly high signal / noise with small overall dimensions of the transducer and free design options in terms of size and number of measuring electrode surfaces. Relationship.
  • the converter according to the invention is thus more sensitive than conventional converters.
  • the construction according to the invention allows a largely free choice of the design of the measuring electrode (s) and thus an adaptation to a wide variety of measuring problems.
  • all membrane types can be used as membranes are used in conventional ion-selective electrodes.
  • the amplifier circuit can also be designed using a wide variety of techniques.
  • the converter can be constructed inexpensively using hybrid technology or thin-film technology, even with small quantities.
  • the carrier plate consists of an insulating material, which can in particular be SiO2, a ceramic material such as Al2O3, glass, an epoxy resin or a plastic material (claim 3).
  • the carrier plate thus not only provides the necessary stability with a small thickness, but also reliably shields the amplifier circuit (s) against environmental influences.
  • a ceramic material such as Al2O3 ceramic is suitable, for example, for applying the material of the measuring electrode, conductor layer and other conductor tracks in thick-film technology.
  • the measuring electrode, the conductor passing through the carrier plate and optionally the conductor layer consist of a material which is chemically inert to the fluid, so that there is no reaction with the fluid to be examined and, in particular, for the application of the membranes practically any auxiliary substances (solvents, Reducing and oxidizing agents, radicals for coupling and polymerizations) allowed.
  • auxiliary substances solvents, Reducing and oxidizing agents, radicals for coupling and polymerizations
  • Such materials are for example gold, platinum, silver, palladium or alloys thereof or a conductive polymer such as e.g. Polypyrrole.
  • the area of the measuring electrode can be limited by a mask plate applied to the carrier plate.
  • This development of the invention has the advantage that a trough-like receptacle with a defined base area is formed for applying the membrane to the measuring electrode, so that the membrane is a has corresponding expansion and its thickness can be determined by simple liquid metering. This also opens up the possibility that the user himself can apply the membrane with sufficient accuracy, which is necessary if sensitive and less stable biological materials such as enzymes and antibodies are to be used as the membrane. Furthermore, it becomes possible to remove used membranes and to reuse the transducer by applying a new membrane.
  • Possible membranes to be applied by the user are specified in claim 13, according to which the membrane can be applied by (electro-) chemical reactions or in dissolved form. Furthermore, it is also possible, according to claim 12, to arrange the mask plate to be removable or replaceable: It is thus possible to arrange the mask plate on the transducer only for applying the membrane or to vary the membrane area by attaching differently designed mask plates.
  • the measure of claim 9, according to which the mask plate covers the bore, is expedient for further protection of the amplifier circuit provided in the encapsulation.
  • the insulator layer covering the bore and provided between the mask plate and the carrier plate also serves to further seal the plated-through hole.
  • This insulator layer can preferably consist of SiO2, polyimide, epoxy resin, aluminum oxide or a silicone resin.
  • the mask plate and the amplifier circuit encapsulating cover made of the material of the carrier plate, so mechanical stresses, which could otherwise lead to leaks due to temperature fluctuations with different thermal expansion coefficients, are avoided.
  • a ceramic in particular forms a good electrical insulator and is chemically inert, ie it does not react with the fluid to be examined and is physiologically indifferent.
  • the pressure filling of the converter housing provided with an inert gas according to claim 15 represents an additional measure for protecting the amplifier circuit against the ingress of water vapor and prevents oxidation of the electronic components, for example during autoclaving processes such as can be carried out with temperature-stable sensors.
  • the sensor channels each consist of a pair of sensors whose potentials are determined with respect to a reference solution contact and subtracted from each other.
  • One electrode surface is coated with the desired membrane, the other with the same, but "carrier-free" mixture.
  • Carrier-free means that the membrane or layer does not have the sensitive component.
  • the difference formation eliminates potential instabilities of the reference solution contact and unspecific matrix effects of the membranes, such as those caused by the diffusion of lipophilic blood lipids.
  • a chemosensitive transducer 10 is immersed in the fluid 11 to be examined and is connected via external supply lines to a voltage supply 12 and a display device 13, which can be a line recorder, for example.
  • the transducer 10 is provided on its surface facing the viewer in FIG. 1 with two pairs of differential sensors 14 and a reference solution contact 15.
  • Each differential sensor pair 14 contains an active sensor 16 and a passive sensor 17.
  • the active and passive sensors of each differential sensor pair 14 are arranged symmetrically with respect to the reference solution contact 15.
  • the sensor 16 then comprises a measuring electrode 19 applied to the upper side of an Al2O3 ceramic carrier plate 18 and a conductor layer 20 is applied opposite to it on the underside of the carrier plate 18.
  • An amplifier circuit 22 is arranged on the conductor layer 20 with the interposition of an SiO2 insulating cut 21, which may be a commercially available integrated circuit and the examples are briefly explained below with reference to FIGS. 4 and 5.
  • the gate of an input field effect transistor of the amplifier circuit 22 is connected to the measuring electrode 19 via a wire 23 and a through-contacting connecting conductor 24.
  • the conductor 24 runs through a microbore which passes through the carrier plate 18 and is produced, for example, by means of a laser beam and has a diameter in the range of less than 0.1 mm.
  • the carrier plate 18 is coated in the relevant surface areas with gold printing paste, with which the microbore is simultaneously filled. When the printing paste burns, a conductive gold layer forms on the wall of the bore.
  • Fig. 3 shows the spatial design of the conductor layer 20, the SiO2 insulating layer 21 applied thereon and the integrated amplifier circuit 22 attached thereon is attached.
  • a mask plate 27 made of Al2O3 ceramic is applied, which has a sensor opening 28 in the area of the measuring electrode 19.
  • the micro-hole penetrated by the conductor 24 is located outside of this sensor opening 28 and is therefore covered by the mask plate 27 and additionally sealed by the SiO2 layer 26.
  • the measuring electrode 19 is coated with a membrane 29 which contains a substance which is sensitive to the chemical property to be detected.
  • the sensor opening 28 formed in the mask plate 27 in conjunction with the measuring electrode 19 provided on the carrier plate 18 forms a trough-like depression with a defined base area.
  • the membrane 29 can therefore be applied very easily in liquid form, with a pre-metered amount of liquid resulting in a membrane of a predetermined thickness.
  • This application method is also suitable for sensitive materials that cannot be applied by conventional methods such as sputtering or vapor deposition.
  • the use of the ceramic mask plates 27 also allows a used membrane to be removed and replaced with a new one, so that the transducer as a whole can be used repeatedly.
  • a passive sensor 17 does not fundamentally differ from the structure described in FIG. 2 for an active sensor 16. He also has a membrane that up on the sensitive component, which makes up about 1% of the membrane mass in the membrane 29 of the active sensor 16, has the same composition.
  • the reference solution contact 15 shown in FIG. 1 differs from the structure shown in FIG. 2 in that the measuring electrode is exposed without a membrane and no separate wiring is provided.
  • the reference solution contact 15, which conveys the reference potential for the entire converter, is connected to the respective amplifier circuit 22 in the manner described below.
  • the measuring electrode 19 and the conductor layer 20 with the ceramic carrier plate 18 located between them form a capacitor which causes a low input capacitance of the converter and a shielding of the high-impedance input signal (in the range of 1015 ⁇ against stray electrical fields.
  • FIG. 2 also shows a cover 30 which encapsulates the amplifier circuit 22 attached to the underside of the carrier plate 18 in connection with the carrier plate 18.
  • the cover 30 is made of Al2O3 ceramic.
  • the noise within the encapsulation is filled with an inert gas under excess pressure in order to counteract the penetration of water vapor from the outside and to prevent oxidation of the electronic components under the influence of temperature.
  • the cover 30 can extend over the entire rear side of the converter 10 shown in FIG. 1 and surrounds the electronics of all sensors 16, 17.
  • the converter can be equipped with two (or even more) pairs of differential sensors 14, with a corresponding choice of the selective substances, the active sensors 16 determine two or more chemical properties of the fluid 11 simultaneously.
  • the active sensor 16 is connected to the input field effect transistor of a first operational amplifier stage 31 and the passive sensor 17 is connected to the input field effect transistor of a second operational amplifier 32.
  • Very high-resistance primary stages (R in ⁇ 1015 ⁇ , I in ⁇ 150 fA) are used for the impedance conversion of the electrode potentials.
  • the low-impedance output signals of the amplifiers 31 and 32 are at the two inputs of a differential amplifier 33, the output signal of which forms the measurement signal.
  • the reference solution contact 15 is coupled via a resistor 34 to the input of the differential amplifier 33 to which the signal from the passive sensor 17 is applied, while a trim input 35 is connected via a further operational amplifier 36 and a further resistor 37 to the input of the Differential amplifier 33 is coupled.
  • the reference solution contact 15 is also connected to the analog earth terminal 38 of the converter.
  • the conductor layer 20 is connected to the output of one of the operational amplifiers 31, 32, so that the impedance-converted input signal is applied to the shielding surface.
  • the circuit shown in FIG. 4 with its essential components forms an example of the amplifier circuit, designated 22 in FIG. 2, which is designed in an integrated form.
  • Figure 6 shows the characteristics of a sensor according to the invention for different ions.
  • the electrode surfaces are sensitized with PVC liquid membranes without restricting the general inventive concept.
  • Membrane mixtures known from the literature can be used for this. According to the difference concept, both a carrier-containing and a carrier-free membrane are used for each type of ion.
  • the geometry of the sensor zone is precisely defined by the electrode mask, so that membranes of the same thickness can be reproducibly produced by simple liquid metering. Since the membranes are fixed to the electrode surface by adhesion, they can be removed again and the sensor module can be re-coated after cleaning.
  • the following table describes the composition of the sensitive membranes for the ions exemplified in FIG. 6.
  • the membrane compositions correspond to the mixtures described for classic ion-selective electrodes.
  • the difference membranes differ from the sensitive membranes in that there is no carrier.
  • the response curves of the above-described sensor for calcium ions according to the invention are shown in partial image (I), in tell image (II) for ammonium ions and in partial image (III) for protons.
  • the response curves of the sub-images I and II apply to aqueous solutions of the chloride salts, the response behavior of the proton sensor is given for 500 mM (filled measuring points) and for 50 mM (unfilled measuring points) sodium phosphate buffer solution.
  • the response time and the determined gradients in the linear range of the sensors are summarized in the partial image (IV).
  • the sensor according to the invention can be used for a wide variety of measurements in the field of medical technology, chemical analysis technology, environmental protection, etc.

Abstract

Chemically sensitive transducer (10) for selectively determining a chemical property of a fluid (11), having at least one field-effect transistor, the gate of which is connected to a corresponding measuring electrode (19) covered with a membrane (29) that is sensitive to said chemical property, and a metal protection (30) which insulates the whole of the transducer (10), except the membran(s) (29), from the fluid (11). Said transducer is characterized in that a supporting plate (18) is provided, the measuring electrode (19) being arranged on one of its sides while an amplifier circuit (22) containing the field-effect transistor is arranged on its other side, and in that the measuring electrode (19) is electrically connected to the gate of the field-effect transistor over a conductor (24) passing through the supporting plate (18).

Description

Technisches GebietTechnical field

Die Erfindung betrifft einen chemosensitiven Wandler zur selektiven Bestimmung einer chemischen Eigenschaft eines Fluids, mit wenigstens einem Feldeffekttransistor, dessen Gate mit einer zugeordneten Meßelektrode verbunden ist, die mit einer für die chemische Eigenschaft sensitiven Membran bedeckt ist, und mit einer Kapselung, die den gesamten Wandler mit Ausnahme der Membran gegenüber dem Fluid isoliert.The invention relates to a chemosensitive transducer for the selective determination of a chemical property of a fluid, with at least one field effect transistor, the gate of which is connected to an associated measuring electrode which is covered with a membrane sensitive to the chemical property, and with an encapsulation which covers the entire transducer with the exception of the membrane isolated from the fluid.

Unter "chemosensitiv" wird drei eine ionen- oder gassensitive Eigenschaft, eine Empfindlichkeit für Enzymsubstrate, für Antikörper/Antigene oder für hydridfähige DNA/RNA-Gruppen verstanden. Je nach ihrer Sensitivität sind derartige Wandler in der Medizin, etwa zur Blutanalyse, in der klinischen Chemie, zur Therapiesteuerung, Hormonbestimmung, Infektions- und Tumordiagnostik, ferner auch in der Fermentationssteuerung, Lebensmittelanalyse, und Umweltanalytlk sowie für Prozeßsteuerungen einsetzbar.“Chemosensitive” means three an ion- or gas-sensitive property, a sensitivity for enzyme substrates, for antibodies / antigens or for hydride-capable DNA / RNA groups. Depending on their sensitivity, such transducers can be used in medicine, for example for blood analysis, in clinical chemistry, for therapy control, hormone determination, infection and tumor diagnosis, and also in fermentation control, food analysis, and environmental analysis, as well as for process control.

Stand der TechnikState of the art

Ein chemosensitiver Wandler mit den im Oberbegriff des Patentanspruchs 1 angegebenen Merkmalen ist aus EP-B-0 065 350 bekannt. Dort ist in einem Halbleitersubstrat ein Feldeffekttransistor ausgebildet, dessen Gate über einen seitlich anschließenden Leiter mit einer auf der gleichen Substratseite angeordneten Meßelektrode verbunden ist. Die Meßelektrode ist mit einer für die zu bestehende chemische Eigenschaft sensitiven Membran bzw. Schicht versehen, die durch Elektroplattieren, Sputtern oder Aufdampfen aufgetragen wird. Der Feldeffekttransistor ist gegen das zu untersuchende Fluid durch eine Schutzschicht abgekapselt, die aus einem Epoxiharz oder Silikonkautschuk besteht.A chemosensitive transducer with the features specified in the preamble of claim 1 is known from EP-B-0 065 350. There, a field effect transistor is formed in a semiconductor substrate, the gate of which is connected via a laterally adjoining conductor to a measuring electrode arranged on the same side of the substrate. The measuring electrode is one for the existing chemical Provide property sensitive membrane or layer, which is applied by electroplating, sputtering or vapor deposition. The field effect transistor is encapsulated against the fluid to be examined by a protective layer which consists of an epoxy resin or silicone rubber.

Wird der so aufgebaute Wandler mit seiner sensitiven Membran in das zu untersuchende Fluid eingetaucht, so entsteht aufgrund von Ionenaustauschreaktionen zwischen der elektroaktiven Substanz der Membran und dem Fluid an der Gate-Elektrode des Feldeffekttransistors ein Potential, das dessen Kanalleitfähigkeit beeinflußt. Durch potentiometrische oder amperometrische Messung läßt sich ein entsprechendes Ausgangssignal gewinnen, das zur Konzentration des zu messenden Parameters proportional ist.If the transducer with its sensitive membrane is immersed in the fluid to be examined, a potential arises due to ion exchange reactions between the electroactive substance of the membrane and the fluid at the gate electrode of the field effect transistor, which influences its channel conductivity. A corresponding output signal can be obtained by potentiometric or amperometric measurement, which is proportional to the concentration of the parameter to be measured.

Weitere chemosensitive Wandler sind aus der EP-A-0 302 228, der EP-B 0 078 590 oder der US-PS 4 514 276 bekannt.Further chemosensitive transducers are known from EP-A-0 302 228, EP-B 0 078 590 or US Pat. No. 4,514,276.

Die durch die genannte Ionenaustauschreaktion hervorgerufene Spannung liegt zwar im mV-Bereich, die ohm'sche Belastbarkeit der Membran liegt jedoch im pA- bis fA-Bereich. Beim Arbeiten mit derart geringen Ladungsmengen kommt es darauf an, daß jegliche Störeinflüsse, insbesondere solche elektrischer oder thermischer natur, ferngehalten werden, wozu die genannten Druckschriften keine Maßnahmen angeben. Eine weitere Schwierigkeit bei den bekannten Wandlern besteht darin, daß sie zum Nachweis nur solcher chemischer Eigenschaften eingesetzt werden können, für die Membranen sensitiv sind, die sich durch die genannten Verfahren auf die Meßelektrode auftragen lassen.The voltage caused by the ion exchange reaction mentioned is in the mV range, but the ohmic load capacity of the membrane is in the pA to fA range. When working with such small amounts of charge, it is important that any interferences, in particular those of an electrical or thermal nature, are kept away, for which the cited documents do not specify any measures. Another difficulty with the known transducers is that they can only be used for the detection of chemical properties for which membranes are sensitive, which can be applied to the measuring electrode by the methods mentioned.

Beschreibung der ErfindungDescription of the invention

Der Erfindung liegt die Aufgabe zugrunde, einen chemosensistiven Wandler anzugeben, der verglichen mit bekannten chemosensitiven Wandlern eine höhere Empfindlichkeit aufweist, und der gleichzeitig gegen elektrische Einflüsse als auch gegen Temperaturschwankungen unempfindlich ist, wobei er auch für solche Eigenschaften sensitiv ausgestalbar sein soll, die sich nur mit wenig stabilen Membransubstanzen nachweisen lassen.The invention has for its object to provide a chemosensitive transducer which has a higher sensitivity compared to known chemosensitive transducers, and which is at the same time insensitive to electrical influences as well as to temperature fluctuations, it should also be sensitive to those properties that can only have it detected with less stable membrane substances.

Eine erfindungsgemäße Lösung dieser Aufgabe ist im Patentanspruch 1 angegeben:
   Erfindungsgemäß ist eine Trägerplatte vorgesehen, auf deren einer Seite die Meßelektrode und auf deren anderer Seite eine den Feldeffekttransistor enthaltende Verstärkerschaltung angeordnet sind; ferner ist die Meßelektrode mit dem Gate des Feldeffekttransistors über einen die Trägerplatte durchsetzenden Leiter elektrisch verbunden.An inventive solution to this problem is specified in claim 1:
According to the invention, a carrier plate is provided, on one side of which the measuring electrode and on the other side of which an amplifier circuit containing the field effect transistor are arranged; furthermore, the measuring electrode is electrically connected to the gate of the field effect transistor via a conductor passing through the carrier plate.

Die Anordnung von Meßelektrode und Verstärkerschaltung auf gegenüberliegenden Seiten einer Trägerplatte mit Durchkontaktierung durch die Trägerplatte hindurch ergibt bei geringen Gesamtabmessungen des Wandlers und freier Gestaltungsmöglichkeit hinsichtlich Größe und Anzahl der Meßelektrodenflächen kürzeste Entfernungen zwischen der jeweiligen Meßelektrode und der zugehörigen Verstärkerschaltung mit einem entsprechend hohen Signal/Rausch-Verhältnis. Damit ist der erfindungsgemäße Wandler empfindlicher als herkömmliche Wandler. Darüberhinaus ist durch den erfindungsgemäßen Aufbau eine weitgehend freie Wahl der Ausbildung der Meßelektrode(n) und damit eine Anpassung an die verschiedensten Meßproblemen möglich. Insbesondere können als Membranen sämtliche Membrantypen verwendet werden, wie sie bei herkömmlichen Ionen-selektiven Elektroden Verwendung finden.The arrangement of the measuring electrode and amplifier circuit on opposite sides of a carrier plate with plated-through holes through the carrier plate results in the shortest distances between the respective measuring electrode and the associated amplifier circuit with a correspondingly high signal / noise with small overall dimensions of the transducer and free design options in terms of size and number of measuring electrode surfaces. Relationship. The converter according to the invention is thus more sensitive than conventional converters. In addition, the construction according to the invention allows a largely free choice of the design of the measuring electrode (s) and thus an adaptation to a wide variety of measuring problems. In particular, all membrane types can be used as membranes are used in conventional ion-selective electrodes.

Ferner kann auch die Verstärkerschaltung in den unterschiedlichsten Techniken ausgebildet sein, beisplelsweise ist ein Aufbau des Wandlers in Hybridtechnik oder Dünnschichtechnik auch bei kleinen Stückzahlen kostengünstig zu realisieren.Furthermore, the amplifier circuit can also be designed using a wide variety of techniques. For example, the converter can be constructed inexpensively using hybrid technology or thin-film technology, even with small quantities.

Weiterbildungen der Erfindung sind in den Unteransprüchen angegeben:
   Gemäß Anspruch 2 besteht die Trägerplatte aus einem isolierenden Material besteht, das insbesondere SiO₂, ein keramisches Material wie Al₂O₃, Glas, ein Epoxidharz oder ein Kunststoffmaterial sein kann (Anspruch 3). Damit sorgt die Trägerplatte nicht nur bei geringer Dicke für die notwendige Stabilität, sondern schirmt auch die Verstärkerschaltung(en) zuverlässig gegen Umwelteinflüsse ab. Ein keramisches Material wie Al₂O₃-Keramik eignet sich beispielsweise dazu, um das Material der Meßelektrode, Leiterschicht und sonstigen Leiterbahnen in Dickschichttechnologie aufzutragen.Further developments of the invention are specified in the subclaims:
According to claim 2, the carrier plate consists of an insulating material, which can in particular be SiO₂, a ceramic material such as Al₂O₃, glass, an epoxy resin or a plastic material (claim 3). The carrier plate thus not only provides the necessary stability with a small thickness, but also reliably shields the amplifier circuit (s) against environmental influences. A ceramic material such as Al₂O₃ ceramic is suitable, for example, for applying the material of the measuring electrode, conductor layer and other conductor tracks in thick-film technology.

Im Anspruch 4 ist gekennzeichnet, daß zwischen der Verstärkerschaltung und der Trägerplatte eine der Meßelektrode gegenüberliegende Leiterschicht angeordnet ist, dieauf das gleiche Potential wie die Meßelektrode gelegt werden kann. Diese Maßnahme führt zu einer aktiven Abschirmung des hochimpedanten Eingangssignals gegen elektrische Störfelder, wodurch das Signal/Rausch-Verhältnis weiter verbessert, die Empfindlichkeitsgrenze des Wandlers herabgesetzt und seine Ansprechgeschwindigkeit erhöht sowie das Übersprechverhalten bei einem Wandler mit mehreren Kanälen verbessert wird. Die Anordnung nach Anspruch 4 bedeutet weiterhin, daß Eingangskapazitäten praktisch vollständig eliminiert werden.In claim 4 it is characterized in that between the amplifier circuit and the carrier plate a conductor layer is arranged opposite the measuring electrode, which can be connected to the same potential as the measuring electrode. This measure leads to an active shielding of the high-impedance input signal against electrical interference fields, which further improves the signal-to-noise ratio, lowers the sensitivity limit of the converter and increases its response speed, and crosstalk behavior in a converter with multiple channels is improved. The arrangement according to claim 4 further means that input capacities are virtually completely eliminated.

Gemäß Anspruch 5 ist zur elektrischen Verbindung zwischen der Meßelektrode und dem Feldeffekttransistor eine die Trägerplatte durchsetzende Bohrung vorgesehen, die einen Durchmesser von weniger als 0,1 mm hat, und die zumindest an ihrer Wandung mit leitendem Material beschichtet ist Diese Weiterbildung der Erfindung hat den Vorteil, daß wegen des geringen Bohrungsquerschnitts ruhende oder schwach bewegte Flüssigkeiten infolge ihrer Oberflächenspannung auch dann nicht an die Verstärkerschaltung gelangen können, wenn die Außenseite der Bohrung freiliegen sollte.According to claim 5 is provided for the electrical connection between the measuring electrode and the field effect transistor through the carrier plate through bore, which has a diameter of less than 0.1 mm, and which is coated at least on its wall with conductive material. This development of the invention has the advantage that because of the small bore cross-section, stationary or weakly moving liquids cannot reach the amplifier circuit due to their surface tension even if the outside of the bore should be exposed.

Nach Anspruch 6 bestehen die Meßelektrode, der die Trägerplatte durchsetzende Leiter sowie gegebenenfalls die Leiterschicht aus einem chemisch gegen das Fluid inerten Material, so daß es keine Reaktion mit dem zu untersuchenden Fluid eingeht und insbesondere für das das Aufbringen der Membranen praktisch beliebige Hilfsstoffe (Lösungsmittel, Reduktions- und Oxidationsmittel, Radikale für Koppelungen und Polymerisationen) gestattet. Derartige Materialien sind beispielsweise Gold, Platin, Silber, Palladium bzw. Legierungen hiervon oder ein leitfähiges Polymer, wie z.B. Polypyrrol.According to claim 6, the measuring electrode, the conductor passing through the carrier plate and optionally the conductor layer consist of a material which is chemically inert to the fluid, so that there is no reaction with the fluid to be examined and, in particular, for the application of the membranes practically any auxiliary substances (solvents, Reducing and oxidizing agents, radicals for coupling and polymerizations) allowed. Such materials are for example gold, platinum, silver, palladium or alloys thereof or a conductive polymer such as e.g. Polypyrrole.

Im Anspruch 8 ist gekennzeichnet, daß die Fläche der Meßelektrode durch eine auf die Trägerplatte aufgebrachte Maskenplatte begrenzt sein kann. Diese Weiterbildung der Erfindung hat den Vorteil, daß zum Auftragen der Membran auf die Meßelektrode eine trogartige Aufnahme mit definierter Grundfläche gebildet wird, so daß die Membran eine entsprechende Ausdehnung aufweist und in ihrer Dicke durch einfache Flüssigkeitsdosierung festgelegt werden kann. Damit wird auch die Möglichkeit eröffnet, daß der Anwender selbst die Membran mit hinreichender Genauigkeit auftragen kann, was dann erforderlich ist, wenn empfindliche und wenig stabile biologische Materialien wie Enzyme und Antikörper als Membrane verwendet werden sollen. Ferner wird es möglich, verbrauchte Membranen zu entfernen und den Wandler durch Aufbringen einer neuen Membran wiederzuverwenden. Mögliche vom Anwender selbst aufzubringende Membranen sind im Anspruch 13 angegeben, gemäß dem die Membran durch (elektro-)chemische Reaktionen oder in gelöster Form aufbringbar ist. Weiterhin ist es gemäß Anspruch 12 auch möglich, die Maskenplatte abnehmbar bzw. austauschbar anzuordnen:
   Damit ist es möglich, die Maskenplatte nur zum Aufbringen der Membran am Wandler anzuordnen bzw. die Membranfläche durch Anbringen unterschiedlich ausgestalteter Maskenplatten zu variieren.In claim 8 is characterized in that the area of the measuring electrode can be limited by a mask plate applied to the carrier plate. This development of the invention has the advantage that a trough-like receptacle with a defined base area is formed for applying the membrane to the measuring electrode, so that the membrane is a has corresponding expansion and its thickness can be determined by simple liquid metering. This also opens up the possibility that the user himself can apply the membrane with sufficient accuracy, which is necessary if sensitive and less stable biological materials such as enzymes and antibodies are to be used as the membrane. Furthermore, it becomes possible to remove used membranes and to reuse the transducer by applying a new membrane. Possible membranes to be applied by the user are specified in claim 13, according to which the membrane can be applied by (electro-) chemical reactions or in dissolved form. Furthermore, it is also possible, according to claim 12, to arrange the mask plate to be removable or replaceable:
It is thus possible to arrange the mask plate on the transducer only for applying the membrane or to vary the membrane area by attaching differently designed mask plates.

Die Maßnahme des Anspruchs 9, gemäß dem die Maskenplatte die Bohrung bedeckt, ist zum weiteren Schutz der in der Kapselung vorgesehenen Verstärkerschaltung zweckmäßig.The measure of claim 9, according to which the mask plate covers the bore, is expedient for further protection of the amplifier circuit provided in the encapsulation.

Auch die gemäß Anspruch 10 zwischen der Maskenplatte und der Trägerplatte vorgesehene die Bohrung abdeckende Isolator-Schicht dient zur weiteren Abdichtung der Durchkontaktierung. Diese Isolatorschicht kann nach Anspruch 11 bevorzugt aus SiO₂, Polyimid, Epoxidharz, Aluminiumoxid oder einem Silikonharz bestehen.The insulator layer covering the bore and provided between the mask plate and the carrier plate also serves to further seal the plated-through hole. This insulator layer can preferably consist of SiO₂, polyimide, epoxy resin, aluminum oxide or a silicone resin.

Sind, wie bei der Ausgestaltung nach Anspruch 14 vorgesehen, auch die Maskenplatte und die die Verstärkerschaltung einkapselnde Abdeckung aus dem Material der Trägerplatte hergestellt, so werden mechanische Spannungen, wie sie sonst infolge von Temperaturschwankungen bei unterschiedlichen Wärmeausdehnungskoeffizienten zu Undichtigkeiten führen könnten, vermieden. Insbesondere eine Keramik bildet darüberhinaus einen guten elektrischen Isolator und ist chemisch inert, d.h. sie reagiert nicht mit dem zu untersuchenden Fluid und ist physiologisch indifferent.Are, as provided in the embodiment according to claim 14, the mask plate and the amplifier circuit encapsulating cover made of the material of the carrier plate, so mechanical stresses, which could otherwise lead to leaks due to temperature fluctuations with different thermal expansion coefficients, are avoided. In addition, a ceramic in particular forms a good electrical insulator and is chemically inert, ie it does not react with the fluid to be examined and is physiologically indifferent.

Die nach Anspruch 15 vorgesehen Überdruckbefüllung des Wandlergehäuses mit einem Inertgas stellt eine zusätliche Maßnahme zum Schutz der Verstärkerschaltung gegen eindringenden Wasserdampf dar und verhindert eine Oxidation der elektronischen Bauteile, etwa bei Autoklavierungsvorgängen, wie sie mit temperaturstabilen Sensoren durchführbar sind.The pressure filling of the converter housing provided with an inert gas according to claim 15 represents an additional measure for protecting the amplifier circuit against the ingress of water vapor and prevents oxidation of the electronic components, for example during autoclaving processes such as can be carried out with temperature-stable sensors.

Die Ausbildung gemäß Anspruch 16, nach der der Wandler wenigstens ein Differenzsensor-Paar mit einer aktiven Meßelektrode und inaktiven Meßelektrode aufweist, umgeht die Notwendigkeit einer externen Referenzelektrode, die aber bei dem erfindungsgemäßen Wandler jederzeit verwendet werden kann. Die Sensorkanäle bestehen jeweils aus einem Sensorpaar, dessen Potentiale bezüglich eines Referenzlösungskontakts bestimmt und voneinander subtrahiert werden. Eine Elektrodenfläche wird mit der gewünschten Membran, die andere mit der gleichen, jedoch "carrierfreien" Mischung beschichtet. Unter "carrierfrei" versteht man dabei, daß die Membran bzw. Schicht die sensitive Komponente nich aufweist. Durch die Differenzbildung werden Potentrialinstabilitäten des Referenzlösungskontaktes sowie unspezifische Matrixeffekte der Membranen, wie sie beispielsweise durch die Eindiffusion lipophiler Blutfette hervorgerufen werden, eliminiert.The embodiment according to claim 16, according to which the converter has at least one pair of differential sensors with an active measuring electrode and inactive measuring electrode, avoids the need for an external reference electrode, which, however, can be used at any time in the converter according to the invention. The sensor channels each consist of a pair of sensors whose potentials are determined with respect to a reference solution contact and subtracted from each other. One electrode surface is coated with the desired membrane, the other with the same, but "carrier-free" mixture. "Carrier-free" means that the membrane or layer does not have the sensitive component. The difference formation eliminates potential instabilities of the reference solution contact and unspecific matrix effects of the membranes, such as those caused by the diffusion of lipophilic blood lipids.

Kurze Beschreibung der ZeichnungBrief description of the drawing

Ausführungsbeispiele der Erfindung werden nachstehend anhand der Zeichnungen näher erläutert. In den Zeichnungen zeigen

  • Fig. 1 eine schematische Darstellung eines chemosensitiven Wandlers im Einsatz,
  • Fig. 2 einen teilweisen Längsschnitt durch den Wandler gemäß Fig. 1,
  • Fig. 3 eine Draufsicht auf die die Verstärkerschaltung tragende Fläche der in Fig. 2 gezeigten Trägerplatte,
  • Fig. 4 und 5 Beispiele für eine elektrische Schaltung zur potentiometrischen bzw. amperometrischen Signalerfassung, und
  • Fig. 6 Kennlinien eines erfindungsgemäßen Wandlers.
Embodiments of the invention are explained below with reference to the drawings. Show in the drawings
  • 1 is a schematic representation of a chemosensitive transducer in use,
  • 2 shows a partial longitudinal section through the converter according to FIG. 1,
  • 3 is a plan view of the surface of the carrier plate shown in FIG. 2 which carries the amplifier circuit,
  • 4 and 5 examples of an electrical circuit for potentiometric or amperometric signal detection, and
  • Fig. 6 characteristics of a converter according to the invention.

Beschreibung bevorzugter AusführungsbeispieleDescription of preferred embodiments

In der in Fig. 1 gezeigten Anordnung taucht ein chemosensitiver Wandler 10 in das zu untersuchende Fluid 11 ein und ist über externe Zuleitungen mit einer Spannungsversorgung 12 und einem Anzeigegerät 13, bei dem es sich bspw. um einen Linienschreiber handeln kann, verbunden.In the arrangement shown in FIG. 1, a chemosensitive transducer 10 is immersed in the fluid 11 to be examined and is connected via external supply lines to a voltage supply 12 and a display device 13, which can be a line recorder, for example.

Der Wandler 10 ist an seiner in Fig. 1 dem Betrachter zugewandten Fläche mit zwei Differenzsensorpaaren 14 und einem Referenzlösungskontakt 15 versehen. Jedes Differenzsensorpaar 14 enthält einen aktiven Sensor 16 und einen passiven Sensor 17. Der aktive und der passive Sensor jedes Differenzsensorpaares 14 sind zu dem Referenzlösungskontakt 15 symmetrisch angeordnet.The transducer 10 is provided on its surface facing the viewer in FIG. 1 with two pairs of differential sensors 14 and a reference solution contact 15. Each differential sensor pair 14 contains an active sensor 16 and a passive sensor 17. The active and passive sensors of each differential sensor pair 14 are arranged symmetrically with respect to the reference solution contact 15.

In der geschnittenen Teildarstellung der Fig. 2 ist einer der aktiven Sensoren 16 mit zugehöriger Elektronik im einzelnen dargestellt. Der Sensor 16 umfaßt danach eine auf der Oberseite einer aus Al₂O₃-Keramik bestehenden Trägerplatte 18 aufgebrachte Meßelektrode 19, der gegenüber auf der Unterseite der Trägerplatte 18 eine Leiterschicht 20 aufgetragen ist.2 shows one of the active sensors 16 with associated electronics in detail. The sensor 16 then comprises a measuring electrode 19 applied to the upper side of an Al₂O₃ ceramic carrier plate 18 and a conductor layer 20 is applied opposite to it on the underside of the carrier plate 18.

Auf der Leiterschicht 20 ist unter Zwischenschaltung einer SiO₂-Isolierschnitt 21 eine Verstärkerschaltung 22 angeordnet, bei der es sich um eine kommerziell erhältliche integrierte Schaltung handeln kann und fair die Beispiele anhand der Fig. 4 und 5 weiter unten kurz erläutert werden.An amplifier circuit 22 is arranged on the conductor layer 20 with the interposition of an SiO₂ insulating cut 21, which may be a commercially available integrated circuit and the examples are briefly explained below with reference to FIGS. 4 and 5.

Das Gate eines Eingangs-Feldeffekttransistors der Verstärkerschaltung 22 ist über einen Draht 23 und einen durchkontaktierenden Verbindungsleiter 24 mit der Meßelektrode 19 verbunden. Der Leiter 24 verläuft durch eine die Trägerplatte 18 durchsetzende, bspw. mittels Laserstrahl hergestellte Mikrobohrung mit einem Durchmesser im Bereich von weniger als 0,1 mm. Zur Herstellung der Meßelektrode 19 und der Leiterschicht 20 wird die Trägerplatte 18 in den betreffenden Flächenbereichen mit Golddruckpaste beschichtet, mit der gleichzeitig die Mikrobohrung aufgefüllt wird. Beim Brennen der Druckpaste bildet sich an der Wandung der Bohrung eine leitende Goldschicht aus.The gate of an input field effect transistor of the amplifier circuit 22 is connected to the measuring electrode 19 via a wire 23 and a through-contacting connecting conductor 24. The conductor 24 runs through a microbore which passes through the carrier plate 18 and is produced, for example, by means of a laser beam and has a diameter in the range of less than 0.1 mm. To produce the measuring electrode 19 and the conductor layer 20, the carrier plate 18 is coated in the relevant surface areas with gold printing paste, with which the microbore is simultaneously filled. When the printing paste burns, a conductive gold layer forms on the wall of the bore.

Fig. 3 zeigt die räumliche Gestaltung der Leiterschicht 20, der darauf aufgebrachten SiO₂-Isolierschicht 21 und der auf dieser angebrachten integrierten Verstärkerschaltung 22. In einer Aussparung der Leiterschicht 20 endet der die Mikrobohrung durchsetzende Verbindungsleiter 24 in einem Anschlußlappen 25, an dem der Bonddraht 23 befestigt ist.Fig. 3 shows the spatial design of the conductor layer 20, the SiO₂ insulating layer 21 applied thereon and the integrated amplifier circuit 22 attached thereon is attached.

Auf der Oberseite der Trägerplatte 18 ist unter Zwischenschaltung einer SiO₂-Schicht 26 eine aus Al₂O₃-Keramik bestehende Maskenplatte 27 aufgebracht, die im Bereich der Meßelektrode 19 eine Sensoröffnung 28 aufweist. Die von dem Leiter 24 durchsetzte Mikrobohrung befindet sich ausserhalb dieser Sensoröffnung 28 und wird daher von der Maskenplatte 27 abgedeckt und zusätzlich durch die SiO₂-Schicht 26 abgedichtet. Im Bereich der Sensoröffnung 28 ist die Meßelektrode 19 mit einer Membran 29 beschichtet, die eine für die nachzuweisende chemische Eingenschaft sensitive Substanz enthält.On the upper side of the carrier plate 18, with the interposition of an SiO₂ layer 26, a mask plate 27 made of Al₂O₃ ceramic is applied, which has a sensor opening 28 in the area of the measuring electrode 19. The micro-hole penetrated by the conductor 24 is located outside of this sensor opening 28 and is therefore covered by the mask plate 27 and additionally sealed by the SiO₂ layer 26. In the area of the sensor opening 28, the measuring electrode 19 is coated with a membrane 29 which contains a substance which is sensitive to the chemical property to be detected.

Wie aus Fig. 2 hervorgeht, bildet die in der Maskenplatte 27 ausgebildete Sensoröffnung 28 in Verbindung mit der auf der Trägerplatte 18 vorhandenen Meßelektrode 19 eine trogartige Vertiefung mit definierter Grundfläche. Die Membran 29 läßt sich daher sehr einfach in flüssiger Form auftragen, wobei eine vordosierte Flüssigkeitsmenge eine Membran vorgegebener Dicke ergibt. Infolge dieser Gestaltung kann das Aufbringen der Membran 29 dem Anwender überlassen werden und kurz vor dem eigentlichen Einsatz erfolgen, was bei kurzlebigen Substanzen von Bedeutung ist. Ferner eignet sich dieses Auftragsverfahren auch für solche empfindlichen Materialien, die nicht durch herkömmliche Verfahren wie Sputtern oder Aufdampfen aufgebracht werden können. Die Verwendung der keramischen Maskenplatten 27 gestattet es ferner, eine verbrauchte Membran zu entfernen und durch eine neue zu ersetzen, so daß der Wandler insgesamt wiederholt verwendet werden kann.As can be seen from FIG. 2, the sensor opening 28 formed in the mask plate 27 in conjunction with the measuring electrode 19 provided on the carrier plate 18 forms a trough-like depression with a defined base area. The membrane 29 can therefore be applied very easily in liquid form, with a pre-metered amount of liquid resulting in a membrane of a predetermined thickness. As a result of this design, the application of the membrane 29 can be left to the user and can take place shortly before the actual use, which is important in the case of short-lived substances. This application method is also suitable for sensitive materials that cannot be applied by conventional methods such as sputtering or vapor deposition. The use of the ceramic mask plates 27 also allows a used membrane to be removed and replaced with a new one, so that the transducer as a whole can be used repeatedly.

Ein passiver Sensor 17 unterscheidet sich von dem in Fig. 2 für einen aktiven Sensor 16 beschriebenen Aufbau grundsätzlich nicht. Auch er weist eine Membran auf, die bis auf die sensitive Komponente, die bei der Membran 29 des aktiven Sensors 16 etwa 1% der Membranmasse ausmacht, die gleiche Zusammensetzung hat.A passive sensor 17 does not fundamentally differ from the structure described in FIG. 2 for an active sensor 16. He also has a membrane that up on the sensitive component, which makes up about 1% of the membrane mass in the membrane 29 of the active sensor 16, has the same composition.

Der in Fig. 1 gezeigte Referenzlösungskontakt 15 weicht dagegen von dem in Fig. 2 gezeigten Aufbau insofern ab, als bei ihm die Meßelektrode ohne Membran freiliegt und keine eigene Beschaltung vorgesehen ist. Der Referenzlösungskontakt 15, der das Bezugspotential für den gesamten Wandler vermittelt, ist in der weiter unten beschriebenen Weise mit der jeweiligen Verstärkerschaltung 22 verbunden.The reference solution contact 15 shown in FIG. 1, on the other hand, differs from the structure shown in FIG. 2 in that the measuring electrode is exposed without a membrane and no separate wiring is provided. The reference solution contact 15, which conveys the reference potential for the entire converter, is connected to the respective amplifier circuit 22 in the manner described below.

In dem Aufbau nach Fig. 2 bilden die Meßelektrode 19 und die Leiterschicht 20 mit der dazwischen befindlichen Keramik-Trägerplatte 18 einen Kondensator, der eine geringe Eingangskapazität des Wandlers und eine Abschirmung des hochimpedanten Eingangssignals (im Bereich von 10¹⁵ Ω gegen elektrische Streufelder bewirkt.2, the measuring electrode 19 and the conductor layer 20 with the ceramic carrier plate 18 located between them form a capacitor which causes a low input capacitance of the converter and a shielding of the high-impedance input signal (in the range of 10¹⁵ Ω against stray electrical fields.

In Fig. 2 ist ferner eine Abdeckung 30 dargestellt, die die an der Unterseite der Trägerplatte 18 angebrachte Verstärkerschaltung 22 in Verbindung mit der Trägerplatte 18 umkapselt. Auch die Abdeckung 30 besteht aus Al₂O₃-Keramik. Der Rausch innerhalb der Umkapselung ist mit einem inerten Gas unter Überdruck gefüllt, um einem Eindringen von Wasserdampf von außen entgegenzuwirken und Oxidation der elektronischen Komponenten unter Temperatureinfluß zu verhindern. Die Abdeckung 30 kann sich über die gesamte Rückseite des in Fig. 1 dargestellten Wandlers 10 erstrekken und umgibt die Elektronik sämtlicher Sensoren 16, 17.FIG. 2 also shows a cover 30 which encapsulates the amplifier circuit 22 attached to the underside of the carrier plate 18 in connection with the carrier plate 18. The cover 30 is made of Al₂O₃ ceramic. The noise within the encapsulation is filled with an inert gas under excess pressure in order to counteract the penetration of water vapor from the outside and to prevent oxidation of the electronic components under the influence of temperature. The cover 30 can extend over the entire rear side of the converter 10 shown in FIG. 1 and surrounds the electronics of all sensors 16, 17.

Dadurch daß der Wandler mit zwei (oder auch mehreren) Differenzsensorpaaren 14 bestückt werden kann, lassen sich bei entsprechender Wahl der selektiven Substanzen der aktiven Sensoren 16 zwei oder mehrere chemische Eigenschaften des Fluids 11 gleichzeitig bestimmen.Because the converter can be equipped with two (or even more) pairs of differential sensors 14, with a corresponding choice of the selective substances, the active sensors 16 determine two or more chemical properties of the fluid 11 simultaneously.

In der Schaltung für potentiometrische Signalerfassung nach Fig. 4 ist der aktive Sensor 16 an den Eingangs-Feldeffekttransistor einer ersten Operationsverstärkerstufe 31 und der passive Sensor 17 an den Eingangs-Feldeffekttransistor eines zweiten Operationsverstärkers 32 angeschlossen. Dabei werden zur Impedanzwandlung der Elektrodenpotentiale sehr hochohmige Primärstufen (Rin ≈ 10¹⁵Ω, Iin ≈ 150 fA) eingesetzt. Die niederimpedanten Ausgangssignale der Verstärker 31 und 32 liegen an den beiden Eingängen eines Differenzverstärkers 33, dessen Ausgangssignal des Meßsignal bildet. Der Referenzlösungskontakt 15 ist über einen Widerstand 34 auf den mit dem Signal des passiven Sensors 17 beaufschlagten Eingang des Differenzverstärkers 33 gekoppelt, während ein Trimmeingang 35 über einen weiteren Operationsverstärker 36 und einen weiteren Widerstand 37 auf den mit dem Ausgangssignal des aktiven Sensors 16 beaufschlagten Eingang des Differenzverstärkers 33 gekoppelt ist. Der Referenzlösungskontakt 15 ist ferner mit der Analog-Erdklemme 38 des Wandlers verbunden. Bei potentiometrischen Betrieb wird die Leiterschicht 20 mit dem Ausgang eines der Operationsverstärker 31, 32 verbunden, so daß das impedanzgewandelte Eingangssignal auf die Abschirmfläche gegeben wird.In the circuit for potentiometric signal detection according to FIG. 4, the active sensor 16 is connected to the input field effect transistor of a first operational amplifier stage 31 and the passive sensor 17 is connected to the input field effect transistor of a second operational amplifier 32. Very high-resistance primary stages (R in ≈ 10¹⁵Ω, I in ≈ 150 fA) are used for the impedance conversion of the electrode potentials. The low-impedance output signals of the amplifiers 31 and 32 are at the two inputs of a differential amplifier 33, the output signal of which forms the measurement signal. The reference solution contact 15 is coupled via a resistor 34 to the input of the differential amplifier 33 to which the signal from the passive sensor 17 is applied, while a trim input 35 is connected via a further operational amplifier 36 and a further resistor 37 to the input of the Differential amplifier 33 is coupled. The reference solution contact 15 is also connected to the analog earth terminal 38 of the converter. In the case of potentiometric operation, the conductor layer 20 is connected to the output of one of the operational amplifiers 31, 32, so that the impedance-converted input signal is applied to the shielding surface.

Die in Fig. 4 mit ihren wesentlichen Bestandteilen dargestellte Schaltung bildet ein Beispiel für die in Fig. 2 mit 22 bezeichnete, in integrierter Form ausgebildete Verstärkerschaltung.The circuit shown in FIG. 4 with its essential components forms an example of the amplifier circuit, designated 22 in FIG. 2, which is designed in an integrated form.

Die Schaltung nach Fig. 5 ist zur amperometrischen Signalerfassung ausgebildet, wobei die gleichen Bezugszeichen wie in Fig. 4 gleiche Schaltungselemente bedeuten. Die unterschiedliche Verdrahtung ergibt sich aus einem Vergleich mit Fig. 4.5 is designed for amperometric signal detection, the same reference numerals as in Fig. 4 mean the same circuit elements. The different wiring results from a comparison with FIG. 4.

Insgesamt weist der vorstehend beschriebene Wandler folgende vorteilhafte Eigenschaften auf:

  • (a) Im Gegensatz zu herkömmlichen Elektroden gestattet der beschriebene Wandler eine Miniaturisierung des Meßsystems und der Membranoberflächen bei weitgehend vari abler Größe und Formgebung. Der Wandler erfordert nur geringe Herstell- und Entwicklungskosten und läßt sich für die unterschiedlichsten Anwendungsfälle gestalten. Die Sensoren weisen kurze Ansprechzeiten auf. Durch Bestücken mit mehreren Sensoren lassen sich gleichzeitig mehrere Parameter messen. Bei Verwendung von mehreren Membranen mit unterschiedlichen Selektivitäten ist eine weitgehende elektronische Eliminierung der Kreuzselektivitäten einzelner Differenzsensorpaare durch eine nachgeschaltete Elektronik möglich. Die Signalerfassung ist in den Wandler integriert, so daß das Ausgangssignal ohne weitere Aufbereitung zur Anzeige verwendet werden kann.
  • (b) Gegenüber herkömmlichen chemosensitiven Feldeffekttransistoren weist der oben erläuterte Wandler infolge seiner Einkapselung keine Haltbarkeitsprobleme auf. Die verschiedensten Membransubstanzen lassen sich leicht aufbringen, und es ergibt sich eine höhere Variabilität in der Kombination der bioselektiven Komponenten. Infolge der größeren möglichen Elektrodenoberflächen lassen sich die Mengen der aufzubringenden Membransubstanzen genauer reproduzieren. Diffusionsprobleme, wie sie bei FET-Multisensoren auftreten, werden vermieden.
Overall, the converter described above has the following advantageous properties:
  • (a) In contrast to conventional electrodes, the transducer described allows miniaturization of the measuring system and the membrane surfaces with largely variable size and shape. The converter requires only low manufacturing and development costs and can be designed for a wide variety of applications. The sensors have short response times. By equipping with several sensors, several parameters can be measured simultaneously. If several membranes with different selectivities are used, extensive electronic elimination of the cross-selectivities of individual differential sensor pairs is possible by means of a downstream electronics. The signal acquisition is integrated in the converter so that the output signal can be used for display without further processing.
  • (b) Compared to conventional chemosensitive field effect transistors, the transducer explained above has no durability problems due to its encapsulation. A wide variety of membrane substances can be easily applied, and there is greater variability in the combination of the bioselective components. As a result of the larger possible electrode surfaces, the amounts of membrane substances to be applied can be reproduced more precisely. Diffusion problems, such as occur with FET multisensors, are avoided.

Figur 6 zeigt die Kennlinien eines erfindungsgemäßen Sensors für verschiedene Ionen. Dabei sind ohne Beschränkung des allgemeinen Erfindungsgedankens die Elektrodenflächen mit PVC-Flüssigmembranen sensitiviert. Dafür können aus der Literatur bekante Membranmischungen verwendet werden. Dem Differenzkonzept entsprechend wird für jede Ionenart sowohl eine carrierhaltige als auch eine carrierfreie Membran verwendet.Figure 6 shows the characteristics of a sensor according to the invention for different ions. The electrode surfaces are sensitized with PVC liquid membranes without restricting the general inventive concept. Membrane mixtures known from the literature can be used for this. According to the difference concept, both a carrier-containing and a carrier-free membrane are used for each type of ion.

Zum Aufbringen der Membranen auf die Elektrodenflächen wird wie folgt vorgegangen: Nach dem Trocknen des Sensors über CaCl₂ werden 7 µl einer 21 %igen Lösung der PVC-Membranen in THF in die entsprechenden Elektrodenmulden pipettiert. Nach dem Verdampfen des THF wird dieser Vorgang wiederholt. Anschließend erfolgt die Konditionierung der Membranen in einem Elektrolytgemisch.To apply the membranes to the electrode surfaces, proceed as follows: After drying the sensor over CaCl₂, 7 µl of a 21% solution of the PVC membranes in THF are pipetted into the corresponding electrode wells. After the THF has evaporated, this process is repeated. The membranes are then conditioned in an electrolyte mixture.

Durch die Elektrodenmaske ist die Geometrie der Sensorzone exakt definiert, so daß durch einfache Flüssigdosierung reproduzierbar Membranen gleicher Dicke hergestellt werden können. Da die Membranen durch Adhäsion auf der Elektrodenfläche fixiert sind, können sie wieder abgezogen und das Sensormodul nach Reinigung neu beschichtet werden.The geometry of the sensor zone is precisely defined by the electrode mask, so that membranes of the same thickness can be reproducibly produced by simple liquid metering. Since the membranes are fixed to the electrode surface by adhesion, they can be removed again and the sensor module can be re-coated after cleaning.

In der folgenden Tabelle ist die Zusammensetzung der sensitiven Membranen für die in Figur 6 beispielhaft angegebenen Ionen beschrieben. Die Membranzusammensetzungen entsprechen bei den für klassische Ionen-selektive Elektroden beschriebenen Mischungen. Die Differenzmembranen unterscheiden sich von den sensitiven Membranen durch das Fehlen des Carriers.

Figure imgb0001
The following table describes the composition of the sensitive membranes for the ions exemplified in FIG. 6. The membrane compositions correspond to the mixtures described for classic ion-selective electrodes. The difference membranes differ from the sensitive membranes in that there is no carrier.
Figure imgb0001

In Figur 6 sind im Teilbild (I) die Ansprechkurven des vorstehend beschriebenen erfindungsgemäßen Sensors für Calcium-Ionen, im Tellbild (II) für Ammonium-Ionen und im Teilbild (III) für Protonen angegeben. Die Ansprechkurven der Teilbilder I und II gelten für wässrige Lösungen der Chloridsalze, das Anspiechverhalten des Protonen-Sensors ist für 500 mM (ausgefüllte Meßpunkte) und für 50 mM (nicht ausgefüllte Meßpunkte) natriumphosphat-Pufferlösung angegenen. Im Teilbild (IV) sind die Ansprechzeiten und die ermittelten Steigungen im linearen Bereich der Sensoren zusammengefaßt.In FIG. 6, the response curves of the above-described sensor for calcium ions according to the invention are shown in partial image (I), in tell image (II) for ammonium ions and in partial image (III) for protons. The response curves of the sub-images I and II apply to aqueous solutions of the chloride salts, the response behavior of the proton sensor is given for 500 mM (filled measuring points) and for 50 mM (unfilled measuring points) sodium phosphate buffer solution. The response time and the determined gradients in the linear range of the sensors are summarized in the partial image (IV).

Gewerbliche AnwendbarkeitIndustrial applicability

Der erfindungsgemäße Sensor kann zu den verschiedensten Messungen im Bereich der Medizintechnik, der chemischen Analysentechnik, des Umweltschutzes etc. eingesetzt werden.The sensor according to the invention can be used for a wide variety of measurements in the field of medical technology, chemical analysis technology, environmental protection, etc.

Claims (16)

  1. Chemically-sensitive transducer (10) for the selective determination of a chemical property of a fluid (11), with at least one field-effect transistor whose gate is connected to an associated measuring electrode (19) that is covered by a membrane (29) sensitive to the chemical property, and with an encapsulation (30) that isolates the entire transducer (10), with the exception of the membrane(s) (29), from the fluid, characterised in that a substrate plate (18) on whose one side the measuring electrode (19) and on whose other side an amplifier circuit (22) containing the field-effect transistor are arranged, is provided, and that the measuring electrode (19) is electrically connected to the gate of the field-effect transistor via a conductor (24) passing through the substrate plate (18).
  2. Transducer according to claim 1, characterised in that the substrate plate (18) consists of an insulating material.
  3. Transducer according to claim 2, characterised in that the substrate plate consists of SiO₂, a ceramic material such as Al₂O₃, glass, an epoxy resin or a plastics material.
  4. Transducer according to claim 2 or 3, characterised in that a conductive layer (20) is arranged opposite to the measuring electrode (19) between the amplifier circuit (22) and the substrate plate (18).
  5. Transducer according to one of the claims 1 to 4, characterised in that a hole which passes through the substrate plate (18), which has a diameter of less than 0.1 mm and whose walls at least are coated with conductive material, is provided for the electrical connection (24) between the measuring electrode (19) and the field-effect transistor.
  6. Transducer according to one of the claims 1 to 5, characterised in that the measuring electrode (19), the conductor (24) passing through substrate plate (18) and, if necessary, the conductive layer (20) consist of a material that is chemically inert with respect to the fluid.
  7. Transducer according to claim 6, characterised in that the material is gold, platinum, silver, copper, palladium or alloys thereof, or a conductive polymer.
  8. Transducer according to one of the claims 1 to 7, characterised in that the area of the measuring electrode (19) is limited by a masking plate placed on the substrate plate (18).
  9. Transducer according to claim 8 in conjunction with claim 5, characterised in that the masking plate (27) covers the hole.
  10. Transducer according to claim 9, characterised in that an insulating layer covering the hole is arranged between the masking plate (27) and the substrate plate (18).
  11. Transducer according to claim 10, characterised in that the insulating layer consists of SiO₂, polyamide, epoxy resin, aluminium oxide or a silicone resin.
  12. Transducer according to one of the claims 1 to 11, characterised in that the masking plate (27) is removable.
  13. Transducer according to one of the claims 1 to 12, characterised in that the membrane (29) can be applied by (electro-) chemical reactions or in a dissolved form.
  14. Transducer according to one of the claims 1 to 13, characterised in that the substrate plate (18), the masking plate (27) and a covering (30) encapsulating the amplifier circuit (22) consist of the same insulating material.
  15. Transducer according to one of the claims 1 to 14, characterised in that the space enclosing the amplifier circuit (22), that is bounded by the substrate plate (18) and a covering (30), is filled with inert gas under a pressure that is above atmospheric pressure.
  16. Transducer according to one of the claims 1 to 15, characterised in that it contains at least one pair of differential sensors with an active measuring electrode and an inactive measuring electrode.
EP89908966A 1988-08-11 1989-08-09 Chemically sensitive transducer Expired - Lifetime EP0382831B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT89908966T ATE85430T1 (en) 1988-08-11 1989-08-09 CHEMOSENSITIVE CONVERTER.

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DE3827314A DE3827314C1 (en) 1988-08-11 1988-08-11
DE3827314 1988-08-11

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EP0382831B1 true EP0382831B1 (en) 1993-02-03

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US (1) US5039390A (en)
EP (1) EP0382831B1 (en)
JP (1) JPH07109413B2 (en)
DE (2) DE3827314C1 (en)
WO (1) WO1990001694A1 (en)

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DE3827314C1 (en) 1989-10-19
DE58903464D1 (en) 1993-03-18
EP0382831A1 (en) 1990-08-22
US5039390A (en) 1991-08-13
WO1990001694A1 (en) 1990-02-22
JPH03502135A (en) 1991-05-16
JPH07109413B2 (en) 1995-11-22

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